1. Field
The disclosure relates generally to voltage regulator circuits and methods and, more particularly, to a low dropout circuit device having improved voltage regulation and a method thereof.
2. Description of the Related Art
Power management unit (PMU) systems utilize voltage regulators to provide a well regulated voltage at the output load. DC-to-DC voltage regulators have different circuit topology, depending on if it is a step-up, or step-down voltage regulator network. DC-to-DC power regulators can include buck converters (e.g. step-down), boost converters (e.g. step-up), buck-buck, and buck-boost regulators. Low dropout (LDO) regulators are a type of voltage regulators used in conjunction with semiconductor devices, integrated circuit (IC), battery chargers, and other applications. Low dropout regulators (LDO) can be used in digital, analog, and power applications to deliver a regulated supply voltage. In voltage regulators, both linear and switch mode, the desired objective is to provide a precise, and well controlled voltage at the load point. A switch mode voltage regulator requires a large filtering capacitor to suppress voltage ripple.
Power management units (PMUs) use low dropout (LDO) regulators to provide good voltage characteristics. In a typical circuit topology, an LDO regulator consists of an error amplifier, pass transistor, and a feedback network contained on a semiconductor chip. The LDO regulator can be defined using bipolar transistors, or metal oxide semiconductor field effect transistors (MOSFETs). For a MOSFET-based implementation, the pass transistor is typically a p-channel MOSFET device. The pass transistor has a MOSFET source connected to voltage VDD, and whose MOSFET drain connected to output voltage, VOUT, and whose MOSFET gate is connected to the output of error amplifier. The error amplifier has a negative input defined as voltage reference input, VREF, and a positive input signal feedback voltage, VFB. The feedback network is connected between the p-channel MOSFET output voltage VOUT, and ground reference VSS. The feedback network 3 can consist of a resistor divider network whose output is the feedback voltage, VFB. All of the active and passive elements are integrated onto the semiconductor chip in the low dropout regulator. The pass transistor, the feedback network, the feedback signal line, and the error amplifier are “local” to each other to provide a small component that is low cost.
As illustrated in FIG. 1, a Power Management Unit (PMU) with a buck-buck voltage regulator is shown. FIG. 1 shows a Power Management Unit (PMU) 10, a remote load point (HOST) 20, an inductor 30, a filtering capacitor 40, a printed circuit board (PCB) track output net 50, a feedback connection 60, and ground connection 70. As illustrated, an inductor 30, and filtering capacitor 40 is connected to the Power Management Unit (PMU) 10 via an electrical connection to the remote load point (HOST) 20. A feedback connection 60 is shown, where a point of the OUTPUT NET track is selected as the feedback for the PMU. It is this location on the OUTPUT NET that the PMU senses for regulating the desired voltage. Due to the non-ideal characteristics of the OUTPUT NET track, the voltage that the PMU senses for regulation is different than the voltage at the remote load point (HOST). In an ideal system, the OUTPUT NET track would have an ideal impedance of zero. In actuality, the OUTPUT NET track is a transmission line, and contains inductive, resistive, and capacitive characteristics. Hence, a voltage drop in the time and frequency domain occurs due to these non-ideal characteristics of the OUTPUT NET track.
As illustrated in FIG. 2, an equivalent model can be shown for the electrical network in FIG. 1. As illustrated in FIG. 2, the electrical network can be represented as an equivalent model for a Power Management Unit (PMU) 10, a remote load point (HOST) 20, an inductor 30, a filtering capacitor 40, a printed circuit board (PCB) track output net 50. The equivalent model for the printed circuit board (PCB) track 50 can be represented as an inductor 52, and a resistor 54. The remote load (HOST) 20 can be represented as an equivalent impedance to ground, whose an equivalent circuit comprises of a capacitor 22, a resistor 24, and a current load generator 26.
In operation mode, when the current generator load 26 is driving a current, the voltage on the OUTPUT NET will experience a voltage drop due to the non-ideal characteristics of the printed circuit board (PCB) track 50. This is understood from the equivalent model resistor 54 of the printed circuit board (PCB) track 50. Additionally, a change in the current generator load 26 current magnitude introduces a voltage drop in the PCB track 50 inductor element 52 due to LdI/dt having a non-zero value. If the feedback connection for the remote feedback loop connection 60 is placed closer to the PMU 10 and filtering capacitor 40 (eg. NET A), a “local” feedback is applied. If the feedback connection for the remote feedback is placed closer to the remote load point (HOST) 20 (e.g. Net B), a “remote” feedback is applied. It is a disadvantage to have the feedback connection for the remote feedback loop connection 60 placed closer to the PMU 10 and filtering capacitor 40 (eg. NET A), due to the non-ideal characteristics of the PCB OUTPUT NET track impedance.
Usage of a remote feedback loop has fundamental disadvantages due to the non-ideal impedance characteristics of the printed circuit board (PCB) track. The introduction of these non-ideal characteristics changes the frequency response of the system, and introduce system instability. With the introduction of poles in the system dispersion relationship, a different characteristic response occurs. Additionally, with the remote feedback large loop, the system is more susceptible to noise coupling. This makes the system more susceptible to electromagnetic interference (EMI), and can introduce system-level electromagnetic compatibility (EMC) issues. And lastly, the printed circuit board (PCB) trace parasitic inductance and resistance can interact with the system capacitance elements (e.g. remote load capacitance) leading to RLC oscillation and ringing issues. This can introduce problems for the control circuit.
Usage of a remote feedback loop due to the non-ideal impedance characteristics of the printed circuit board (PCB) track can be addressed with the introduction of a low pass filter (LPF) on the remote feedback loop. As illustrated in FIG. 3, a low pass filter (LPF) to ground is highlighted on the remote feedback net. As illustrated in FIG. 3, the electrical network can be represented as an equivalent model for a Power Management Unit (PMU) 10, a remote load point (HOST) 20, an inductor 30, a filtering capacitor 40, a printed circuit board (PCB) track output net 50, a ground connection 70, a remote feedback line 80, and a low pass filter (LPF) 90. The equivalent model for the printed circuit board (PCB) track 50 can be represented as an inductor 52, and a resistor 54. The remote load (HOST) 20 can be represented as an equivalent impedance to ground, whose an equivalent circuit comprises of a capacitor 22.
In the filtering method, a common filter is the RC low pass filter. Usage of a remote feedback loop due to the non-ideal impedance characteristics of the printed circuit board (PCB) track can be addressed with the introduction of a low pass filter (LPF) on the remote feedback loop. As illustrated in FIG. 4, a low pass filter (LPF) to ground is highlighted on the remote feedback net. The electrical network can be represented as an equivalent model for a Power Management Unit (PMU) 10, a remote load point (HOST) 20, an inductor 30, a filtering capacitor 40, a printed circuit board (PCB) track output net 50, a ground connection 70, a remote feedback line 80, and a low pass filter (LPF) 90. The equivalent model for the printed circuit board (PCB) track 50 can be represented as an inductor 52, and a resistor 54. The remote load (HOST) 20 can be represented as an equivalent impedance to ground, whose an equivalent circuit comprises of a capacitor 22. The low pass filter 90 is shown as a capacitor 92, and a resistor element 94.
In this circuit topology, as illustrated in FIG. 4, a problem still exists with the introduction of a “pole” in the circuit frequency response (e.g. in the circuit dispersion relationship). This approach can be effective in preventing the ringing and the noise coupling to the PCB track net, but does not eliminate the modification of the frequency response of the network.
In power converter circuits, the remote load control has been a concern. As discussed in published U.S. Pat. No. 7,368,831 to Boeckmann, describes an apparatus for sensing and controlling remote load voltages, where the apparatus includes a power converter, a plurality of remote loads, where each remote load located in a loop connected to the power converter. A feedback loop connected to the power converter is physically adjacent to the power converter, and said feedback loop comprises of a first and second path where the two paths are in a parallel configuration.
In switching power converters, solutions for remote response has been addressed. As discussed in U.S. Pat. No. 6,580,256 to Martindale et al., a switching power converter discloses a first electrical device, a second electrical device, a differential amplifier, a feedback loop, an adaptive power supply, and a remote sense feedback amplifier.
In boost power converters, apparatus and method of boosting remote nodes have been discussed. As discussed in U.S. Patent Application 2002/0070717 to Pellegrino, discloses an apparatus and method for boosting power supplied to remote nodes shows an amplifier, a remote active boost regulator, a remote sense, and a feedback loop.
In these prior art embodiments, the solution to improve the voltage regulation introduce complexity, cost, and additional circuitry.